The present invention relates to a natural gas fuel metering assembly for a natural gas engine and in particular to a metering assembly that is conveniently mounted to an engine block and has temperature and pressure sensors positioned in the fuel stream immediately before the fuel injectors to provide pressure and temperature sensing of the fuel at the point of metering.
Heavy duty natural gas engines, such as those used in school buses and urban transit buses, are typically natural gas conversions of diesel engines. The engines share many components with the diesel engine from which it is derived. One such component is the engine block. The diesel engine fuel system is replaced with a fuel system designed to deliver the gaseous fuel, i.e. natural gas, to the engine. The natural gas fuel system includes a metering assembly having a plurality of natural gas fuel injectors. The injectors are opened and closed electronically to control the quantity of fuel being delivered to the intake manifold of the engine. The injectors are disposed between a fuel inlet manifold and a fuel outlet manifold and function to control the quantity of fuel flowing from the inlet to the outlet manifold. From the outlet manifold the fuel is delivered to the combustion air intake manifold.
Upstream of the fuel metering assembly, a temperature sensor and a pressure sensor are placed in the fuel supply line. The output signals of the temperature and pressure sensors are used by the fuel control system to controls the injectors, thereby controlling the quantity of fuel delivered to the engine based on the temperature and pressure at the point of metering. In many natural gas engines, the fuel metering assembly is attached to the side of the engine block wherever space permits. In addition, the pressure and temperature sensors upstream of the metering assembly are not close enough to the injectors to provide an accurate measurement of the natural gas temperature and pressure at the point of metering.
The present invention provides an improved natural gas fuel metering assembly that overcomes the disadvantages of previous natural gas metering assemblies. The present invention provides for the temperature and pressure sensors to be mounted in the intake manifold and senses the natural gas temperature and pressure immediately prior to the natural gas flowing into the injectors.
The metering assembly of the present invention further provides improved mounting of the assembly by utilization of the existing, industry standard, diesel fuel injector pump mounting flange on the cast block. By mounting the natural gas fuel metering assembly to the existing diesel injector pump flange, the need for a separate cover for the diesel injector pump flange is eliminated and an esthetically pleasing mounting of the fuel metering assembly results.